Impact of active intra-complex rest intervals on post-back squat versus hip thrust jumping potentiation

This study investigated the impact of active rest intervals within a lower body complex training session on post-activation performance enhancement (PAPE) response in amateur soccer players. Twelve soccer players took part in four different experimental conditions. These sessions included 2 sets of lower body complex-paired exercises, each involving 3 repetitions of either back squats or hip thrusts at 90% one-repetition maximum (1RM) as a conditioning activity paired with a broad jump and countermovement jump. Between those exercises in active intra-complex rest interval conditions, participants were performing 8 repetitions of bench press at 75%1RM or, in passive intra-complex rest interval conditions, rested while seated. A significant main effect of a set to increase broad jump length (p = 0.002), countermovement jump height (p = 0.002), and modified reactive strength index (p = 0.005) was revealed, without any significant differences between conditions. Post-hoc comparisons showed a significant increase in broad jump length from baseline to Set-2 (231 ± 13 vs. 234 ± 13 cm; p = 0.003; ES = 0.22). On the other hand, countermovement jump height and modified reactive strength index significantly increased from baseline to Set-1 (34.4 ± 3.6 vs. 35.6 ± 3.9 cm; p = 0.027; ES = 0.31 and 0.4 ± 0.05 vs. 0.45 ± 0.09; p = 0.005; ES = 0.66). Results of this study showed that to sustain a high training density, sports practitioners may incorporate upper body exercises within the intra-complex rest interval during lower limb complex training sessions and still elicit a significant PAPE effect.

substantial effect on its occurrence.To the best knowledge of the authors, only Trybulski et al. 13 has evaluated the use of an active inter-complex rest interval during an upper-limb PAPE complex.The authors did not show any impact of body-weight Swiss ball leg curls as an active inter-complex rest interval on post-bench press bench press throw potentiation.Insufficient research has been conducted on lower-limb PAPE complexes and the use of high-intensity exercises during active inter-complex rest intervals.Moreover, interestingly, a recent study by Bartolomei et al. 16 demonstrated that the PAPE effect potentially could occur remotely.Bartolomei et al. 16 showed an increase in countermovement jump (CMJ) power output after a high-intensity bench press.Theoretically, the non-localized PAPE effect may be associated with an increase in epinephrine and norepinephrine levels following high-intensity exercise 17 .Therefore, in this scenario, implementing a high-intensity upper-body exercise within a PAPE complex may even contribute to enhancing the PAPE effect.
Although the PAPE effect has been studied extensively and it is recommended to couple CA and post-CA in terms of their biomechanical similarity, research on this aspect is still lacking 18,19 .According to this principle, when comparing the effectiveness of inducing the PAPE effect through two different CAs involving the same muscle groups, the one that also requires force production in the same direction as the post-CA may be more efficient.For example, SQ should be more effective for potentiation tasks involving lower limb exercises where force is generated vertically, such as vertical jumping.Conversely, hip thrusts (HT) should be superior for potentiation tasks requiring horizontal force generation, such as broad jumps (BJ) or sprints.Interestingly, Seitz et al. 20 demonstrated post-SQ BJ potentiation, but the authors did not evaluate the effectiveness of HT as a CA, so there is uncertainty as to whether the effect would be greater after them, considering the principle of similarity.Meanwhile, neither Atalag et al. 18 nor Carbone et al. 19 demonstrated a significant improvement in sprint performance after SQ or HT.Despite the fact that during the HT, the generated force vector is comparable to that during sprinting.However, there is a dearth of research comparing the effects of SQ and HT on the PAPE effect in both horizontal and vertical jumps.
Considering the above, by comparing the impact of active and passive intra-complex rest intervals, as well as the alignment of exercises with the dynamic correspondence principle, this study aims to shed light on optimal strategies and examines the trade-off between training density and PAPE magnitude.Therefore, this study examined the effects of bench press exercises implemented within the lower body PAPE complex on the magnitude of this phenomenon, specifically SQ and HT as a CA and CMJ and BJ as post-CA tasks.Moreover, the secondary aim was to compare post-SQ and post-HT vertical and horizontal jumping potentiation.It was hypothesized, that performing bench presses will not affect PAPE response and that SQ will be superior in potentiating CMJ performance while HT in BJ length.

Results
Reliability results are described in Table 1.

Discussion
The main objective of this study was to determine the effects of active intra-complex rest intervals inside the lower-body PAPE complex on the occurrence and magnitude of this effect, as well as to compare post-SQ and post-HT CMJ and BJ potentiation in soccer players.This study did not reveal any significant differences in the lower limb PAPE effect between active intra-complex rest interval compared to passive intra-complex rest interval.Similarly, there were no significant differences in the CMJ and BJ enhancements, regardless of whether SQ or HT was used as the CA.Although the differences were not significant, it should be emphasized that the magnitude of the PAPE effect was greater when passive intra-complex rest interval was employed, and when the exercises within the complex were aligned with the dynamic correspondence principle (i.e., HT paired with BJ and SQ paired with CMJ).Therefore, for maximizing the lower limb PAPE effect, we recommend the use of passive intra-complex rest interval.On the other hand, to maintain high training density, sports practitioners may also incorporate upper body exercises within the active intra-complex rest interval during lower limb PAPE.This approach can be utilized, for instance, during periods when a high training volume is required, such as in the preseason when the emphasis is placed on resistance training, or in situations where the available time for training is limited.However, they should be aware that the PAPE magnitude may be reduced.Alternating sets of resistance exercises involving different parts of the body (i.e., lower and upper body muscles) have been used in resistance training for a long time and have been identified as a successful method to increase training density without impacting athletic performance 13,[25][26][27] .Although a complex training method is well studied and its low time efficiency due to the need for long rest periods after the CA (4-8 min) has been indicated as their disadvantage, not much research has been done that has looked for solutions to this drawback [11][12][13] .To the best of the authors' knowledge, this is the second study yet that has evaluated the effect of employing an active intra-complex rest interval during PAPE complexes 13 , and probably the first in the case of the lower limbs.Study by Trybulski et al. 13 did not show an impact of applying active intra-complex rest intervals on the upper-body PAPE effect magnitude.Similarly, this study's findings revealed no differences between the examined conditions.Nonetheless, it should be noted that although statistically insignificant, larger effect sizes were observed in the conditions with passive intra-complex rest intervals for certain variables.Specifically, the enhancement in BJ length after HT-NA was moderate (g = 0.33 in Set-1 and g = 0.45 in Set-2 compared to baseline), whereas after HT-A it was either small (g = 0.14 in Set-1) or not observed (g = 0.00 in Set-2).Similarly, Table 2. Comparison of pre-and post-CA jumping performance.BA-baseline; CA-conditioning activity; CI-confidence interval; SQ-A-squat conditioning with an active rest interval; SQ-NA-squat conditioning without an active rest interval; HT-A-hip thrust conditioning with an active rest interval; HT-NA-hip thrust conditioning without an active rest interval.regarding the RSImod in the SQ-NA condition, the enhancement in Set-2 was large (g = 0.9) and moderate in the SQ-A condition (g = 0.54).These disparities between the current study and the study by Trybulski et al. 13 may have been influenced by the fact that Trybulski et al. 13 applied velocity loss control during CA, individually adjusting its volume and controlling the level of induced fatigue.In contrast, the CA in this investigation consisted of constant CA variables through sets of 3 repetitions at 90% 1RM.Despite the growing popularity of velocitybased training, velocity-controlling devices are still not widely used, so we chose this protocol to enhance the ecological value of this study.In conclusion, the results of this study and the study by Trybulski et al. 13 indicates that applying active intra-complex rest intervals in the form of exercises targeting a distinct body region within the PAPE complex still allows for benefiting from the PAPE effect.As stated previously, there is a lack of investigations on the utilization of active intra-complex rest intervals in PAPE complexes; however, there are studies evaluating the local and non-local occurrence of this phenomenon 14,16 .On one hand, the PAPE effect seems to have a local nature and is associated with mechanisms such as increased muscle temperature or muscle fiber water content in the exercised muscle groups 2 .On the other hand, the non-local PAPE effect may be explained by the elevation of catecholamine concentration due to high-intensity CA 17 .In this scenario, for instance, the combination of SQ or HT as a CA and bench press during active-intra complex rest interval, as in this study, theoretically may even induce a greater PAPE effect in subsequently performed jumps.However, this wasn't the case in this study.The results on this matter are contradictory; for example, Cuenca-Fernandez et al. 14 did not reveal significant differences in the effectiveness of three different CAs, namely, 4 repetitions of SQ, 4 repetitions of bench press, and a combination of both, in eliciting the PAPE effect assessed by squat jumps.Nevertheless, similarly to the findings of this study, Cuenca-Fernandez et al. 14 noted a lower magnitude of the PAPE effect in protocols involving bench press.In contrast, Bartolomei et al. 16 demonstrated improved CMJ absolute power output after 5 sets of a single bench press repetition at 90% 1RM.However, it is important to emphasize that in the Bartolomei et al. 16 study, participants performed CMJ only at the 12th and 14th minutes after the CA, whereas in this study and the study by Cuenca-Fernandez et al. (2017) participants performed CMJ at the 6th, 5th and 8th minute, respectively.Furthermore, the volume and intensity scheme used for bench press in this study did not align with the guidelines to induce the PAPE effect and differed significantly (single set of 8 repetitions at 75%1RM vs. 5 sets of single repetitions at 90%1RM) from those employed by Bartolomei et al. 16 .Interestingly, another study by Bartolomei et al. 25 also demonstrated a significant increase in absolute CMJ power output after bench press (using the same conditioning activity as in their other study 16 ).However, no such effect was reported in the bench press throw after the same back squat protocol (5 sets of a single repetition at 90%1RM).Therefore, it appears that the local PAPE effect may be linked to the amount of muscle mass involved in the conditioning activity, suggesting that the non-localized effect is also associated with it 25,26 .During the active inter-complex rest interval conditions, both BS and HT as well as bench presses were utilized, resulting in a larger muscle area being engaged compared to Bartolomei et al. 16,25 studies.This could potentially explain why the PAPE effect was attenuated.However, it is worth noting that a non-local PAPE effect might become evident in later time frames than the local PAPE effect or if different bench press variables were utilized.
Studies directly comparing SQ vs. HT as CAs on the PAPE phenomenon are limited to evaluating their impact on sprint performance and vertical jumping 18,19 .However, there is a lack of information on whether the PAPE effect induced by these exercises as CAs would differ for vertical and horizontal jumping performance.One of the fundamental principles of PAPE suggests that the CA and post-CA should have a similar movement structure, considering the range of motion, muscle activity, and force production vector 27,28 .This study found no significant differences in the CMJ and BJ enhancements, regardless of whether SQ or HT was used as the CA.Although, similarly to the type of intra-complex rest intervals, the effect size was insignificantly larger when HT-NA was used before BJ compared to SQ-NA (g = 0.33-0.45 vs. g = 0.07-0.31),and conversely, SQ-NA before CMJ (g = 0.38-0.48)compared to HT-NA (g = 0.13-0.14).The observed patterns suggest that a principle of similarity between CA and post-CA may exist.Because HT requires more hip extension, and force expression remains high as the hip approaches full extension [29][30][31] , it appears that HT may be more specific for tasks that require high force expression, such as when the hip nears full extension (as in a BJ).However, the modest results obtained in this study do not strongly support this hypothesis.Further research is needed to clarify the relationship between exercise specificity and force production for optimal utilization of the post-activation potentiation effect.
Despite providing valuable practical insights for athletes and instructors utilizing the PAPE effect in their training, this study should be evaluated in light of its limitations.First, the PAPE effect was only evaluated over two sets of complexes in this study's protocol, so it is unknown how athletic performance would change over consecutive sets.In addition, this study did not include physiological measurements or biomechanical analyses (such as comparing a hip joint range of motion during SQ, HT vs. CMJ and BJ), so we cannot precisely explain why these results were observed.The participants in our study were moderately trained soccer players; therefore, extending these results to other groups should be done with caution.This study highlights the need for future research on the application of active intra-complex rest intervals in PAPE complexes, including implementation over long-term interventions.In addition, it emphasizes the importance of investigating the non-local PAPE effect along with establishing its underlying mechanisms.

Conclusions
This study did not reveal any statistically significant differences in the lower body PAPE effect when comparing an active intra-complex rest interval to a passive intra-complex rest interval.Likewise, there were no significant variations in CMJ and BJ enhancement, regardless of whether SQ or HT was applied as the conditioning activity.While the differences were not statistically significant, it is important to highlight that the magnitude-based effect sizes were greater when a passive intra-complex rest interval was employed and when the exercises within www.nature.com/scientificreports/and 0.0.80 as "large." 40 The smallest worthwhile change (SWC, calculated using formula 0.2 × test-values standard deviation) 41 was used to define whether revealed differences are practically meaningful. https://doi.org/10.1038/s41598-023-47042-7

Table 1 .
Intersession reliability and smallest worthwhile change of the analyzed variables.